Many thermoplastic polymers when thermoformed by casting or molding, and especially injection molding, calendering and extrusion, and the like, have smooth, glossy surfaces. While such surfaces are highly desirable in many applications, there are certain cases wherein they are distinctly disadvantageous. For example, glossy surfaces resist painting because the paints, inks and varnishes tend not to adhere; smooth surfaces mar and abrade, developing a hazy appearance; smooth thermoplastic surfaces tend to stick together when stacked--the so-called blocking phenomenon--, and smooth surfaces reflect light. Light reflection, especially, is a problem because this can cause operators of business machines molded with glossy surfaces to become tired after prolonged usage, because stray light is reflected into their eyes.
Thermoplastics for which surface altering is especially needed are those which injection mold into high strength pieces having highly glossy surfaces. These include the engineering thermoplastics, such as aromatic polycarbonates, aromatic polyester carbonates, aromatic polysulfone carbonates, mixtures thereof and the like, alone, or combined with polyesters of aliphatic or cycloaliphatic diols, or mixtures of such diols, and aromatic dicarboxylic acids, and/or vinyl aromatic polymers, co-polymers or terpolymers, such as polystyrene, rubber modified polystyrene, styrene maleic anhydride copolymers; styrene-acrylonitrile-butadiene terpolymers, mixtures of the foregoing and the like. Business machine housings, especially cathode ray tube housings, and picture tube protective shields, molded from such polymers have a high specular gloss at 60 degrees, according to ASTM Standard Test Method D 523, and a significant reduction in such gloss is desirable, while still maintaining all of the other valuable properties of such materials, especially srrength and flame retardancy, in certain embodiments.
Previous approaches to altering the surface of thermoplastics have involved the use of additives or mechanical treatments such as calendering or sandblasting. The mechanical treatments cannot generally be used in injection molding and extrusion processes. With respect to the additive approach, this generally comprises using inorganic particulate materials, such as calcium silicates, magnesium silicates, amorphous silica gels and the like. Although these work rather well in plasticized poly(vinyl chloride) resins, they are difficult to compound into the high melting engineering thermoplastics which are used in high quality business machine housings, and the like. The difficulty is in obtaining uniformly dispersed particles on the surface of the articles so that predictable gloss reduction is obtained, while at the same time not reducing physical strength. Other additives have been proposed, selected from organic polymeric materials. Canadian Pat. No. 1,049,185, for example, describes cross-linked acrylate polymers, and states that they are useful in a wide range of thermoplastics, including polycarbonates and mixtures thereof, but then goes on to state that the cross-linked polymer should be particulate in form, having an average particle size of 1 to 30 microns. This causes the same difficulty in dispersion and nonuniform gloss-reduction as is commonly experienced when particulate inorganic additives are employed and the resulting composition is injection molded and/or extruded. A further approach suggested for use in poly(vinyl chloride) compounds used in house siding and other rigid profile extrusions, is to blend into the vinyl halide resin a small amount of an impact modifier, such as ethylene-vinyl acetate copolymer and then to add a dulling agent. In a Technical Bulletin on terpolymer resin modifiers, ELVALOY 837 and 838, the DuPont Company has suggested that if a terpolymer of ethylene, vinyl acetate and carbon monoxide is used in poly(vinyl chloride) a desirable matte finish can be obtained without dulling agents. Compositions comprising such terpolymers and a wide variety of other resins, especially poly(vinyl chloride) resins, but including polycarbonates and polyesters, are taught in Hammer, U.S. Pat. No. 3,780,140, but there is no suggestion therein that molded articles having reduced gloss can be obtained without a dulling agent.
It has now been discovered that aromatic polycarbonate resins and modified such resins, alone, or in combination with other resins, can be altered in surface appearance by adding a terpolymer of ethylene, a carbon monoxide and a third monomer. This is unexpected because experiments have shown that without carbon monoxide in the additive, no surface altering is achieved, i.e., gloss is not reduced. The latter such compositions are described in Baron, et al., U.S. Pat. No. 4,145,373 and U.K. Pat. No. 1,508,567. Moreover, the present compositions are almost always compounded above 500.degree. F. and the additives are taught not to be stable at such temperatures.